Humans but not muroid rodents express group 1 CD1 molecules, CD1a, b, and c. Interestingly, group 1 CD1 molecules are closely tied to anti-mycobacterial immunity because they can present a variety of mycobacteria-derived lipid antigens and group 1 CD1-specific T cell responses are detected at higher frequencies in Mycobacterium tuberculosis (Mtb) infected individuals. However, due to the lack of a small animal model, there is no direct evidence of the protective capacity of group 1 CD1-restricted T cells. Therefore, my lab generated a transgenic mouse model (hCD1Tg) that harbored the human group 1 CD1 locus and supported the development of group 1 CD1-restricted T cells. Infection of hCD1Tg mice with Mtb generated group 1 CD1-restricted Mtb lipid antigen-specific T cell responses. In addition, adoptive transfer of group 1 CD1-restricted T cells conferred protection against infection. Taken together, these data indicate that group 1 CD1-restricted T cells play a role in adaptive immunity to Mtb and could serve as vaccine targets. This proposal seeks to further elucidate the role of group 1 CD1-restricted T cells in different stages of Mtb infection and evaluate whether group 1 CD1-restricted T cells play a role in immunity against other bacterial pathogens. In aim 1, we will evaluate whether memory group 1 CD1-restricted T cells can be generated in secondary Mtb infection and whether group 1 CD1-restricted T cells can be activated during latent TB infection. While group 1 CD1-restricted Mtb lipid antigen-specific T cells are present during early stages of Mtb infection, autoreactive group 1 CD1-restricted T cells expand at later stages in the lung of infected mice. In aim 2, we will evaluate the surface phenotype, functional properties of these cells and determine whether they play a protective role during Mtb infection. The group 1 CD1-restricted microbial lipid antigens identified thus far are mainly of mycobacterial origin. There is relatively little known about the role group 1 CD1-restricted T cells play in immunity against other bacterial pathogens. We have selected Staphylococcus aureus (SA) because it is one of the most frequently isolated pathogens associated with nosocomial infections and SA contains several lipids that share common features with CD1-binding antigens. In aim 3, we propose to assess the kinetics, expansion, and function of group 1 CD1-restricted T cells in the context of a systemic SA infection and identify the structure of stimulatory SA lipid antigens. Collectively, these studies will lead to a better understanding of how group 1 CD1-restricted T cells contribute to protective immunity against Mtb and SA and whether they can be targeted for the development of lipid antigen-based vaccines.